This invention falls under the general field of aircraft seats. It relates more specifically to the structure of the seats that are installed in the cockpit or the cabin of an aircraft. Still more specifically, but not in a limiting way, the objects of the invention are seats that are particularly suited to helicopters. Such seats are installed either in the pilot compartment or in a rear position for the passengers of the helicopters.
The design of such seat structures is subject to several requirements, including ergonomic requirements and requirements with regard to safety.
Actually, the normal accelerations to which the aircraft are subjected and the taking into account of extreme cases, such as various crash conditions, call for a mechanical strength for the structure in a large number of cases of static and dynamic loads for which the integrity of the structure of the seats during the use of the aircraft must be ensured.
The seat structures must also provide a certain number of functionalities necessary within the framework of their use (height adjustment/angle of the seat pan and/or of the seatback, of the armrests, of the headrest . . . ).
Taking these constraints into account necessitates the use of devices involving a considerable increase in the weight of the seats. Now, one of the problems of aircraft is to reduce weight as much as possible to save energy necessary for the flight of the aircraft, as well as its performance, without reducing the level of safety of the onboard devices for which the formal requirements are becoming increasingly restrictive.
To respond to these various requirements, there are known within the field of seat structures, in particular for technical seats, various solutions (FIGS. 1 to 5) that are or have been applied, often adapted to one aircraft type or a particular aircraft environment.
A first known device (FIG. 1) uses a telescopic column. In this solution, a seat is integral with a tube with a vertical axis placed under the seat, sliding in a base fastened to the floor of the aircraft. The height adjustment is obtained by extension or retraction of two or more tubes sliding into one another. Their mounting ensures the rigidity of the lower part of the structure of the seat. The holding in position is ensured by a mechanical lock or a braked actuator incorporated into the assembly. The base is adapted to the interfaces of the support of the seat, for example by specific fastening points or by means of two parallel tracks provided with regularly spaced attachment points. The upper part of the seat, for example a bucket made of one or more articulated parts, is designed and adapted to the upper end of the column.
A second known device is of the parallelogram type.
In a first variant (FIG. 2), the feet are fastened to the support of the seat, generally by means of additional structures. These feet are articulated so as to allow an oscillation inducing the variation in height of the upper part along an arc and simultaneously a forward/rearward movement.
In a second variant (FIG. 3), the principle is similar, but the rotation points of the feet are located, offset toward the rear, in such a way that the vertical movement does not induce a notable forward/rearward movement, bearing in mind the vertical adjustment amplitudes.
The center line distance of the feet is a function of the interfaces with the support of the seat on the floor.
A third known seat structure is of the pantograph type (FIG. 4). In this arrangement, the crossed feet are connected to the support of the seat by means of an interface structure. They are articulated at each of their ends. Two of these articulations are associated with a sliding system to make possible the deformation of the pantograph and the vertical movement of the upper part of the seat.
A fourth known solution uses a console-type mounting (FIG. 5). In this solution, the low structure, composed of guide tubes or fittings and of triangulation bars, is connected to the support of the seat on the floor in a conventional way.
The upper part of the seat is integral with the lower structure and can be moved vertically along the fittings or guides. The width of the upper part is directly a function of the distance between the lower guide fittings or tubes.
The height adjustment and maintenance are ensured by a lock system connecting the lower and upper parts.
The inclination of the seatback is also controlled by a lock system that rests on the lower structure.
All of these solutions exhibit a certain complexity with numerous mechanical parts. Furthermore, because of their philosophy of attachment of the structure to the bottom of the seat and of preserving possibilities for adjustment of the vertical position, they exhibit difficulties for ensuring the resistance to longitudinal or vertical stresses, which can be compensated for only by an oversizing of the parts, which increases the total weight of the seat.
Another category of conventional solution is the rear column-type mounting, for example as described in U.S. Pat. No. 4,525,010 of Trickey, Netherway and Clifford of June 1985. In this mounting, the seat is attached by its seatback to two lateral tubes that are approximately vertical or slightly inclined rearward, while having the possibility of sliding along these tubes within the framework of a vertical position adjustment of the seat. These tubes are integral with the floor and with the ceiling of the cockpit of the aircraft. A shock absorber placed between the two lateral tubes, and integral, on the one hand, with the lateral tubes by its upper part, and, on the other hand, with the seat by its lower part, makes it possible to respond to vertical crash stresses.
Specialized seats mounted today in the cockpits of various helicopters have adopted this type of mounting, which makes possible the incorporation of numerous functionalities (height adjustment and angle of the seat pan, forward/rearward adjustment in the flight direction, systems for compensations of movements, dynamic absorption in the case of a crash, systems for attenuation of vibrations . . . ).
The various known variants of rear mountings are all based on the principle of two lateral structures rising on each side of the seatback of the seat bucket of the seat and making possible a good structural strength of the latter in the vertical, longitudinal, and lateral, with the various associated torsional moments. However, these systems have the drawback, on the one hand, of requiring a significant number of parts for each function, since it is necessary to duplicate each system on the two lateral structures, and therefore here again to generate weight, and, on the other hand, to link the complex structure of the seat associated with the different technical constraints to the width of the seat that depends essentially on ergonomic requirements and on the space available in the aircraft for the installation of the seat.